Only the Bolt and Edge on TE4 have the 15 second pre-roll ads that play before a dvr recording. Also Tivo has to have sold some ads in your area or else you just get a quick grey screen with a grey arrow before your recording starts. You can skip the ads by pressing the FFD button.
I also don't see any quick gray screen with arrow. On some shows I set a preroll of 2 minutes and the recording does start at the end of a previous show. On preroll 0 it starts in the middle of a break between the shows on the hour or half hour.
Do you actually witness this or just repeating posters on the TIVO Community? I don't disbelieve it but something seems most inconsistent, like an experimental time TIVO may be testing the acceptance with a few regions.
Note your own linked reference " TiVo’s been trialing " "Trialing" tells me it is being rolled out in select groups of customers or regions and that's why some of us aren't seeing it.